Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
  • B01D53/1425—Regeneration of liquid absorbents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
  • B01D53/1487—Removing organic compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
  • B01D53/1493—Selection of liquid materials for use as absorbents
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/40—Capture or disposal of greenhouse gases of CO2
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/151—Reduction of greenhouse gas [GHG] emissions, e.g. CO2

Definitions

• the present invention relates to a two stage flash process for the effective removal of hydrocarbons in an ethylene oxide process carbon dioxide removal system whereby the amount of flash gas required to remove a certain amount of hydrocarbon in a carbonate removal system is substantially reduced as compared to conventional practices.
• the reaction gas contains a substantial concentration of unreacted ethylene, and in the process of absorbing the carbon dioxide a certain amount of this unreacted ethylene is dissolved in the absorbent solution.
• the solution is directly steam stripped to release the carbon dioxide, the dissolved ethylene contained therein is released to the atmosphere with the stripped carbon dioxide.
• the release of ethylene is disadvantageous in that the permissible amount of ethylene released to the atmosphere is limited by local atmospheric pollution regulations.
• the ethylene has a value as a feed stock. Therefore, it is required and desirable to remove dissolved ethylene from the absorber solution and recover this ethylene.
• a single stage flash is employed to flash the absorber solution with the flashed vapor passing to a recovery compressor in order to recover ethylene for recycle to the process.
• the regulations on ethylene emissions often specify a fixed quantity of ethylene which can be released to the atmosphere independent of plant size. As the plant size increases it is, therefore, often the case that the percent removal required for the ethylene significantly increases with increased plant size, to maintain the absolute emission limit. As the percent removal increases, the amount of flash gas required per unit of ethylene increases and the amount of recycle carbon dioxide also increases.
• the amount of recycle carbon dioxide in a single stage flash system can exceed 20% of the normal carbon dioxide removal requirement and the recovery compressor size can become disproportionately large compared to a smaller plant.
• the use of a two stage flash system can significantly reduce this problem, thus reducing the cost of the carbon dioxide removal system and also the cost and energy consumption of the recovery compressor.
• the ' enriched absorber solution from hot carbonate scrubbing of ethylene oxide reaction gas after the ethylene oxide removal, which enriched solution is high in bicarbonate and which contains dissolved ethylene, is passed from the absorber to a first flash zone wherein the bulk of the dissolved ethylene, oxygen, and other gases are removed from the liquid by flashing into the gas phase.
• the liquid from the first flash zone is sent to a second flash zone wherein conditions of the flashing are controlled to insure that such ethylene as remains in the liquid from the second flash after flashing carbon dioxide and ethylene will meet the appropriate emission regulations when the liquid is steam stripped to release carbon dioxide.
• the hot carbonate absorber liquid from the absorber which is rich in bicarbonate and contains dissolved ethylene and oxygen is passed from the carbon dioxide absorption (not shown) to the first stage flash zone or drum 11 and introduced therein via line 1.
• This absorber liquid is generally at a temperature of about 85°C to 110°C.
• conditions are suitably maintained at an intermediate pressure between the pressure in the absorber which generally is about 18.5 kg/cm 2 absolute to 23.0 kg/cm 2 absolute and atmospheric pressure to provide for flashing into the vapor phase of the bulk of the dissolved oxygen and ethylene and other dissolved gases.
• An illustrative pressure range in the first stage flash is 2.5-4.5 kg/cm 2 absolute.
• the flash vapor from the first stage zone is removed by means of line 3 and passes to the second stage of conventional recovery compressor 20. It is advantageous to have the pressure of the first stage flash vapor match the second stage pressure of the recovery compressor but this is not a requirement. Although the bulk of dissolved ethylene is removed at this point, i.e. at least 80%, and preferably at least 85%, the removal is not controlled in the first stage flash to meet emissions regulations.
• the liquid from the first stage flash zone 11 passes via line 2 to a second stage flash zone 10. In the second stage flash zone 10 the pressure and the flashed vapor rate is controlled to ensure that ethylene remaining dissolved in the liquid from the second flash zone after vapor separation will meet the required regulations when subsequently steam stripped from the liquid during carbon dioxide release. Illustrative pressures for the second stage flash are 1.5-2.5 kg/cm 2 absolute.
• the flashed vapor from zone 10 is removed via line 4 and is preferably passed to the first stage of the recovery compressor 20 for recovery of ethylene in this flash as well as the ethylene in the vapor flashed from the first zone.
• compressor 20 the flash vapors are compressed to reactor pressure and recycled to the ethylene oxide reactor (not shown) via line 21.
• the liquid from the second stage flash zone 10 passes via line 5 to regenerator 12 where carbon dioxide along with dissolved ethylene which remains is stripped from the liquid by conventional means with a combination of live steam introduced via line 7 and reboiler steam from reboiler 13 which is introduced via line 9.
• the liquid from the regenerator which is now lean in bicarbonate and rich in carbonate is returned to the absorber via line 8 for further use in the overall process.
• the carbon dioxide along with water vapor and any residual ethylene is vented from regenerator 12 to the atmosphere via line 6.
• the amount of ethylene vented in this vent stream is maintained at a level so as to comply with the appropriate regulations, usually less that 5.0 kg/hr, and frequently less than 3.0 kg/hr.
• the operating conditions for the two flash stages be optimized.
• the ethylene content of the liquid from the second stage flash must be low enough to meet environmental regulations.
• the liquid from the second stage flash must contain the net carbon dioxide formed in the ethylene oxide reaction in order to avoid carbon dioxide build up.
• Example Rich solution from the absorber at a temperature of about 91 °C and a pressure of about 22.8 kg/cm 2 absolute and containing 97 kg/hr of ethylene passes at a rate of 21 ,700 kg-mol/hr via line 1 to zone 11 and is flashed to a pressure of 3.15 kg/cm2 absolute, in the first stage flash zone 11.
• a flash gas of 349 kg/hr containing 83.1 kg/hr of ethylene and 180 kg/hr of CO is send via line 3 to the recovery compressor 20.
• the liquid from the first stage flash still contains 13.9 kg/hr ethylene which exceeds the emission limit of 2 kg/hr.
• This liquid is sent via line 2 to the second stage flash zone 10 which operates at a pressure of 2.02 kg/cm2 absolute.
• the flashed gas from the second stage is removed at the rate of 120 kg/hr and contains 12.0 kg/hr of ethylene as well as 174 kg/hr of CO 2 .
• This flash gas is sent via line 4 to the recovery compressor 20.
• the liquid from the second stage flash contains residual ethylene of 1.9 kg/hr, a level which meets the target emissions requirement.
• This liquid is sent to the regenerator where the net carbon dioxide of 10,300 kg/hr from the ethylene oxide reaction system is removed and vented to the atmosphere along with the 1.9 kg/hr ethylene.
• the two stage flash procedure of the invention removes a total of 95.1 kg/hr of ethylene (98.0%) and recycled 354 kg/hr of CO 2 or about 3.4% of the net CO 2 production.
• the flow to the recovery compressor system is 589 kg/hr for the combined first and second stage flash zones.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Analytical Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Epoxy Compounds (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Gas Separation By Absorption (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
• Treating Waste Gases (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)
• Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
• Carbon And Carbon Compounds (AREA)

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• 2001
  • 2001-06-05 US US09/874,732 patent/US6533843B2/en not_active Expired - Lifetime
• 2002
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  • 2002-05-17 WO PCT/US2002/015836 patent/WO2002098541A1/en active Application Filing
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• 2003
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